Aims. We discuss observational evidence that quasars play akey role in the formation of galaxies, starting from the detailed studyof the quasar HE0450-2958 and extending the discussion to a series ofconverging evidence that radio jets may trigger galaxy formation. Methods. We use mid infrared imaging with VISIR at the ESO-VLTto model the mid to far infrared energy distribution of the system andthe stellar population of the companion galaxy using optical VLT-FORSspectroscopy. The results are combined with optical, CO, radiocontinuum imaging from ancillary data. Results. The direct detection with VISIR of the 7kpcdistant companion galaxy of HE0450-2958 allows us to spatially separatethe sites of quasar and star formation activity in this compositesystem made of two ultra-luminous infrared galaxies (ULIRGs), where thequasar generates the bulk of the mid infrared light and the companiongalaxy powered by star formation dominates in the far infrared. No hostgalaxy has yet been detected for this quasar, but the companion galaxystellar mass would bring HE0450-2958 in the local -relation if it were to merge with theQSO. This is bound to happenbecause of their close distance (7kpc) and low relative velocity (60-200kms-1). We conclude that we may be witnessing the building of the -relation, or at least of a major event in that process. The star formation rate (340yr-1), age (40-200Myr) and stellar mass ([5-6]1010)are consistent with jet-induced formation of the companion galaxy. Wesuggest that HE0450-2958may be fueled by fresh material from coldgas accretion from intergalactic filaments. We map the projected galaxydensity surrounding the QSO as a potential tracer of intergalacticfilaments and discuss a putative detection. Comparison to other systemssuggest that an inside-out formation of quasar host galaxies andjet-induced galaxy formation may be a common process. Two tests areproposed for this new paradigm: (1) the detection of offset moleculargas or dust emission with respect to the position of distant QSOs; (2)the delayed formation of host galaxies as a result of QSO activity,hence the two step building of the /ratio. Key words: galaxies: active - galaxies: formation - galaxies: jets - galaxies: quasars: individual: HE0450-2958
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